An individual difference (machine difference) of a fuel injector is held in a specified standard in a manufactory. As shown in JP-2006-200378A, the individual difference information is marked on the fuel injector by using of QR code (trademark). When the fuel injector is assembled to an engine, a control unit (ECU etc.) reads the QR code in order to perform an individual-difference correction.
However, in some regions, a reading device for reading the QR code and a writing device for writing the QR code are not spread enough. In such regions, the individual-difference correction by using of the QR code can not be conducted.
In such a case, it is necessary to enhance the individual difference accuracy of the fuel injector, which increases a manufacturing cost of the fuel injector.
In a case that the individual-difference correction of the fuel injector can not be conducted, an output difference arises between cylinders. Thus, a torque fluctuation become large, a fuel consumption is deteriorated, and an engine vibration and an engine noise become large.
Furthermore, when an inferior fuel is used, the fuel injector may be deteriorated. Even if the individual difference is corrected before a shipment, the individual difference may arise due to the deterioration of the fuel injector.
Meanwhile, based on the fuel pressure detected by a fuel pressure sensor provided to a common-rail, the individual-difference correction of the fuel injector may be conducted. However, a fuel injection quantity has dispersion in each injection, which is referred to as a shot-dispersion. Thus, the fuel pressure in the common-rail does not become stable, so that the individual-difference correction is difficult to be conducted.
Further, when the engine load is high, the individual-difference correction can not be conducted.
Due to the above reasons, the individual-difference correction based on the common-rail pressure can not be practically conducted.